tucker ate chocolate last night and we called the e-vet. They said they need to eat about 15oz of pure dark chocolate for them to have an ill effect. They said his stool might get loose and he might vomit. If he/she has eaten that much I would call an e-vet to see what they have to say.
Take a look through my old posts and you will find the topic. SharonL suggested peroxide to make them vomit it up, she has explained how much to give a 3 month old 22lb so hopefully you can judge by that.